Stretch hood packaging systems use a tubular film to bundle and protect goods. The goods may be a single item, such as a washing machine or refrigerator, or a collection of items, such as bottles, bags of soil, bags of polymer pellets, or concrete blocks. Often the goods are supported on a pallet or other supporting platform to form a palletized load which can be easily handled and transported with a forklift. A stretching device stretches the tubular film around the item or items to be packaged forming the stretch hood. As the stretching device releases the stretch hood, the elastic contraction of the film tube around the item(s) provides integrity and stability to the palletized load. The stretch hood can also act to protect and shield the palletized load from damage and environmental factors (e.g., moisture) during transportation and storage. Moreover, the elastic properties of the pallet stretch hood enable it to stabilize goods of different shapes and sizes.
Stretch hood packaging systems may provide certain advantages over other packaging systems such as shrink hood, where a film tube is shrunk by the application of heat, or stretch wrap where a flat film is wrapped around the object or collection of objects to be packaged. Shrink hood films often contain a highly oriented polymer, such as low density polyethylene (“LDPE”), which allows the film to shrink as heat is applied. The shrinking process can consume a significant amount of energy and the high temperatures needed to shrink the film can create safety concerns. Additionally, as the shrink hood film is shrunk it tends to thicken and become stiff. Moreover, shrink hood films are not designed to stretch easily prior to heat shrinking. Stretch wrap films typically comprise a more linear polymer, such as linear low density polyethylene (“LLDPE”). A tackifying polymer or other ingredient is usually added to the stretch wrap film to establish sufficient cling force on the surface of the film. Stretch wrap films are relatively thin and are designed to stretch easily to considerable levels of over 200%. However, the additives needed to provide the film with sufficient cling force on the surface of the film can lead to roll blocking where the stretch wrap film clings to itself when rolled up. Additionally, wrapping a loaded pallet with a linear stretch wrap film can take a significant amount of time and there is often a waste of materials resulting from overlapping layers of the stretch wrap film. Furthermore, the stretch wrap film may only provide incomplete protection against environmental factors.
Different film structures have been suggested for stretch hood films. For example, U.S. Patent Application Publication No. 2006/0040075 discloses a polymer composition comprising a polyolefin, an ethylene acid copolymer, and an ethylene methyl acrylate copolymer for use in packaging materials such as pallet stretch hoods.
PCT Publication WO 2005/014672 discloses multi-layer stretch hood films comprising a core layer containing EVA having a low vinyl acetate content and skin layers comprising linear low density polyethylene.
PCT Publication WO 2006/076917 discloses stretch hoods formed from a biaxially oriented tubular film having a seam. The tubular film may comprise a core layer of an EVA and skin layers of linear low density polyethylene or EVA.
PCT Publication WO 2007/044544 discloses multi-layer elastic air quenched blown film structures having at least two layers. The first layer incorporates a propylene-based copolymer and optionally, a linear low density polyethylene or a low density polyethylene. The second layer incorporates a linear low density polyethylene and optionally, a propylene-based copolymer and/or a low density polyethylene. Alternatively, the second layer may contain an in-reactor blend of a substantially linear polyethylene (or a homogeneously branched linear polyethylene) and a linear low density polyethylene.
While there are many known film structures for stretch hood packaging systems, there remains a need for a stretch hood film that has improved properties and performance in stretch hood packaging systems. Desirably the film will have a better balance between stretchability and holding force. The film should provide package integrity and transparency, resistance to puncture and tearing, and/or reduced stress relaxation at higher ambient temperatures after the stretch hood packaging operation has been completed. Additionally, it would be desirable to have a stretch hood film that has increased “softness”, i.e., the film has increased elasticity and enough holding force to adequately contain the palletized goods but is not so high as to damage the items on the palletized load. Desirably, the film is a single-sized film that can be applied to pallets of different sizes and shapes.